Our invention relates to prosthetic heart valves, and in particular to prosthetic heart valves which are combined with an integral vascular graft for use in replacing a diseased aortic valve and a portion of the aorta of a patient.
Prosthetic heart valves replace diseased valves in a human heart. These valves fall generally into two categories. Biologic valves are comprised of a stent supporting three circumferential leaflets made of a flexible material. If the material is biologic in nature, it may be either a xenograft, that is, harvested from a non-human cadaver, or an allograft, that is, harvested from a human cadaver. Non-biologic material such as polyurethane might also be used.
The second major category of prosthetic heart valves is mechanical valves. These valves usually comprise a rigid annulus supporting one, two or three rigid leaflets. The annulus and leaflets are frequently formed in pyrolitic carbon, a particularly hard and wear resistant form of carbon. The annulus is captured within a sewing ring so that the valve may be attached to heart tissue at the location of the replaced valve.
Functioning valves are critical to the proper action of the heart. If a valve becomes diseased, it may be replaced by a prosthetic valve. If degeneration of a valve has occurred, however, it is likely that surrounding blood vessels are also diseased. Particularly in the case of the aortic valve, surgeons have found that not only the valve but also the adjacent aorta degenerate. Consequently, both valve and a segment of the ascending aorta may be replaced at the same time. In 1968 Bentall and DeBono described a method for attaching a commercially available graft to a Starr-Edwards mechanical heart valve for the complete replacement of an aneurysmal aorta and aortic valve. See, "A Technique for Complete Replacement of the Ascending Aorta", Thorax, 1968; V. 23, pgs. 338-339. After implanting the mechanical heart valve, a surgeon would stitch a segment of vascular graft to the sewing ring of the mechanical valve. The juncture between the valve and the graft was abrupt and there was usually a sharp change of diameter to be expected between the valve and the graft.
Subsequently, Shiley Corp., in conjunction with cardiovascular surgeons, produced a composite valve and preattached graft. Between the valve and the graft, there was a relatively long, tapered fabric section. It was suggested that the taper would provide a smooth transition between the valve and the graft to reduce turbulent flow. Tapered sections of 8 to 12 millimeters have been widely used by Shiley and others offering composite valve/graft combinations.
The combined valves/grafts with the extended tapered section have been effective, but have presented certain drawbacks. The method of attaching the graft inside the sewing ring requires that the valve be generally smaller than that which a surgeon would ordinarily implant. For example, a typical tapered valve/graft combination would employ a valve with the same internal orifice area as 25 millimeter aortic mechanical valve combined with a 27 millimeter sewing ring and a 30 millimeter graft. This results in a restriction in the available flow area, with associated resistance to flow. Further, fabrication of the tapered section has usually been accomplished by means of long pleats. The coronary arteries, which supply blood to the heart, enter the aorta immediately downstream from the aortic valve. These arteries must be reattached to the graft, so that blood can be supplied to the heat. The pleats in a tapered section frequently act as an obstruction to the attachment of the ostia of the coronary arteries. Moreover, since the diameter of the tapered section is usually smaller than either the graft or the aorta that is being replaced, it may be necessary to stretch the coronary arteries, putting additional strain on these critical structures.
With the foregoing in mind, it is an objective of our invention to provide a combined mechanical heart valve and graft which has an expanded valve orifice, corresponding to the diameter of the associated graft.
It has been a further object of our invention to provide a combined heart valve and graft wherein the graft is attached to the valve with little or no transitional taper.
Another object of our invention has been to provide a combined heart valve and graft wherein the graft is immediately adjacent the valve, to provide attachment sites for the ostia of the coronary arteries.
Another object of our invention has been to produce a combined heart valve and graft wherein the graft is attached to the heart valve between the annulus of the valve and the sewing ring.
These and other objects and features of our invention will be apparent from the following description taken with reference to the accompanying drawings.